docs: adding faq (open-telemetry#1068)

Adding an FAQ section, which can also serve as a quick reference.

Not having such a section makes common scenarios harder to discover.

Author: toumorokoshi

docs/faq-and-cookbook.rst

@@ -0,0 +1,27 @@
+Frequently Asked Questions and Cookbook
+=======================================
+
+This page answers frequently asked questions, and serves as a cookbook
+for common scenarios.
+
+Create a new span
+-----------------
+
+.. code-block:: python
+
+    from opentelemetry import trace
+
+    tracer = trace.get_tracer(__name__)
+    with tracer.start_as_current_span("print") as span:
+        print("foo")
+        span.set_attribute("printed_string", "foo")
+
+Getting and modifying a span
+----------------------------
+
+.. code-block:: python
+
+    from opentelemetry import trace
+
+    current_span = trace.get_current_span()
+    current_span.set_attribute("hometown", "seattle")

docs/index.rst

@@ -62,6 +62,7 @@ install <https://pip.pypa.io/en/stable/reference/pip_install/#editable-installs>
     :name: getting-started
 
     getting-started
+    faq-and-cookbook
 
 .. toctree::
     :maxdepth: 1